In a large bowl, combine the cabbage and carrots. Pour 4 cups boiling water over the vegetables and toss. Let sit for 10 minutes, then drain.
Add the vinegar, oregano, and 2 tsp salt. Pour over the slaw. Add green onions and shredded kimchi. Thoroughly mix. transfer the mixture and any leftover liquid in the bowl to an airtight jar or container. Chill for at least 1 hour in the refrigerator or overnight for best results.
To make the chicharrón filling, heat the vegetable oil in a large pan over medium-high heat. Add the pork shoulder and salt. Cook for 15 minutes. If the pork is browning too quickly, reduce the heat to medium. Turn the pork over and let cook on the other side for 10 minutes more, or until crispy and golden brown.
Once cool. Transfer the pork to a food processor. Add gochujang and onion. Pulse until a thick paste forms. Add shredded cheese, refried beans and mix well. Set aside.
NOTE: The next 3 steps can be skipped if you choose to buy premade masa. To make the masa: In a large bowl. Mix together the masa harina and salt, then add the water. Use your hands to mix until the dough comes together to form a clay-like dough.
Fill a small bowl with 3 cups cold water and a tablespoon of oil and set near your work station. You’ll wet your fingers with the mixture as you work to keep the dough from sticking to your hands.
Take a golf ball-sized portion of masa and roll into a ball, then flatten into an even round.
Fill the dough round with 1 tablespoon chicharron filling, Fold the dough over the filling until it’s completely sealed. Then, pat out the ball between your hands until flat. If the pupusa cracks, patch it with a bit of dough and a little oil. Repeat with the remaining ingredients.
Heat a large pan or griddle over medium heat. Brush with vegetable oil, then place 2 pupusas on the pan and cook for 2-4 minutes, or until the bottoms are golden brown. Flip and cook on the other side for 2-4 minutes more, until golden brown and warmed through. Repeat with the remaining pupusas.
Serve pupusas immediately with the Kimchi curtido & desired hot sauce